A disabled man who was incorrectly found fit for work under the government's disability benefit assessment is launching a legal action against the government and Atos, the private company performing the tests. Patrick Lynch, a former social care worker who was forced to stop work because of a condition affecting his brain, is seeking a judicial review of the controversial "work capability assessment". More than 11,000 disabled people a week are taking the tests, which involve interviews with Atos doctors and nurses to identify those who can work.

Charities and disabled groups say the assessment is "not fit for purpose", with appeals against 40% of claims that are turned down. They cite cases of suicide where the coroner has said denial of benefits was a contributory factor. The BBC's Panorama this year found a case of a man who died of heart failure just 39 days after being found fit for work.

Lynch, the first individual to sue over the assessment, is claiming that the government and Atos failed to record an interview despite assurances from ministers that all could be taped.

Atos has 11 audio machines shared between 123 assessment centres despite the then employment minister Chris Grayling in February telling MPs that "we will offer everyone who wants it the opportunity to have their session recorded". In his first interview in September 2010 Lynch was found fit for work – despite five months undergoing brain surgery. Lynch disputed Atos's conclusion. A clinical examination by Atos found "no abnormalities or tenderness to the neck or spine" in spite of the fact he had recently had major surgery. Atos's clinical findings did not record his medical history. "I had been in hospital and lost 54kg (8.5 stone) in weight. The doctors told me I was on death's door. I mean I came in on crutches and could not pick things up because I was afraid of falling over. But they did not say that. I even photocopied my medical notes and handed them over but because there was no recording it was my word against theirs."

Eventually Lynch reversed the Department of Work and Pensions decision and got £100 in compensation for the "stress" he suffered. At his reassessment this year he asked for the interview with Atos to be recorded but was told "no recording equipment was available, that much of it was broken or being used outside of London and that it would take too long to obtain". In his lawsuit, Lynch argues that ministers and the company acted unlawfully in failing to provide enough devices to record sessions.

"That's why I am launching my legal action. You cannot have Atos and the government carrying on like this." Lynch has been backed by False Economy, the anti-cuts campaign funded by the TUC. A spokesperson for False Economy said its investigations had shown that "too many people feel vulnerable in this process. People feel that their final assessment reports inaccurately reflect information exchanged during work capability assessments. We've found it hard to pin down the DWP on recording policy. Universal recording, and giving people the opportunity to see their WCA reports before final eligibility decisions are made, will go some way towards restoring fairness and accuracy while the WCA process continues."

Lynch's solicitor Tessa Gregory of Public Interest Lawyers says that the "assessment process... constitutes an unacceptable risk of unfairness. We hope these safeguards will be instituted to help mitigate that risk."

The TUC general secretary Brendan Barber said: "Assessments of disability must be fair and proportionate, treat people with respect and be part of a consistent system. There is overwhelming evidence that they have fallen far short of these basic standards. It is right that they should be challenged in court."

A DWP spokesperson said it had until 24 December to respond to the lawyer's letter from Lynch Its own most recent review found the "work capability assessment is not in need of fundamental reform. There is a long history of judicial reviews concerning welfare reform and as always we will robustly defend our policies. We have already made substantial improvements to the process."